Change logic for header fragments on the wiki

[cl8n]

currently when you have a page like this, where some headers have the same name:

# Something
## Section
# Something Else
## Section

the generated url fragments for the level 2 headers are #section.1 and #section.2, respectively. it would be more helpful for wiki editors if they were #something.section and #something-else.section instead, because then we wouldn't have to worry about updating them whenever a new header with the same name is added to the page. in the (rare and probably nonexistent) case that the entire path of parent headers is the same, it could fallback to the old behavior

so basically just this format for all headers

# Header        => #header
## Section      => #header.section
### Sub-section => #header.section.sub-section

suggesting this as a solution for my comment here ppy/osu-wiki#2482 (comment)